The present invention relates to a method and apparatus for the control and mixing of a limited volume of fluid when subjected to centrifugal force, for example in the rotor of a centrifugal analyzer.
The present invention is especially suitable for use in centrigual analyzers such as have been conventionally used for a number of years for chemical analysis, especially in clinical chemistry. Such analyzers are especially characterized by their relatively simple mechanical construction and, consequently, great dependability. In general, they have circular, symmetrically-constructed rotors with a plurality of radial flow canals which connect several chambers. Usually, each flow canal has, from the inside towards the outside, a trough-shaped reagent chamber, a sample chamber and a measurement chamber which, in the case of the known devices, is constructed as an optical cuvette. The reagent chamber and the sample chamber are usually filled with a liquid reagent and sample to be investigated (usually blood serum or plasma) while the rotor is stationary. Thereafter, the rotor is rotated comparatively rapidly (on the order of 1000 r.p.m.) so that the reagent is forced centrifugally through the flow canal into the sample chamber and the sample and reagent flow together through the continuation of the flow canal into the optical cuvette. During the rotation of the rotor, the optical absorption of the sample and reagent reaction mixture is measured in the various cuvettes by means of appropriate detectors and an electronic circuit which synchronizes the detectors to the rotation of the rotor. A special advantage of centrifugal analyzers is that the course of the reaction in each cuvette of the rotor can be monitored practically simultaneously and an especially exact evaluation is then, in particular, possible when the kinetics of the reaction give the desired information regarding a particular component of the sample fluid. The principle of the centrifugal analyzer is known from numerous publications so that a detailed description thereof is not necessary here.
However, a disadvantage of the known centrifugal analyzers is that they only permit relatively simple courses of reaction. As described above, one or, in exceptional cases, several reagent fluids are mixed in one operating step with the sample and transported by centrifugal force into the cuvette. Therefore, the reaction must, of necessity, by a one-stage reaction which means, in particular, that there is no possibility of first allowing a pre-reaction to take place with a first reagent and then, possibly after an appropriate incubation time, of carrying out a second reaction with a further reagent. However, such two-stage reactions are of considerable importance, especially in clinical analysis. Federal Republic of Germany Patent Specification No. 20 09 993 describes, in connection with another problem, a device which permits a control, i.e. an interruption, aimed liberation and deflection, of a fluid flow in a device of the initially mentioned type. In this known device, the flow canal for the fluid is provided with hollow chambers which, in each case, are connected by a syphon-like canal with the subsequent hollow chamber. That part of the syphon which lies closest to the axis of rotation is closer to this than the fluid level in the hollow chamber during rotation of the rotor. Only the hollow chamber and the subsequent part of the syphon-like canal are thereby first filled with the fluid. The further flow of the fluid from the hollow chamber into the chamber following the syphon is brought about by applying an appropriate gas pressure to the hollow chamber, which forces the fluid through the syphon. The introduction of the necessary pressurized gas to the rotor can only take place in its center and is, of necessity, expensive to construct. It requires a special rotor design, due to which the construction of the rotor is, in other regards, subject to undesired limitations.
Federal Republic of Germany Patent Specification No. 20 22 084 describes a device in which a fluid, for example blood, is, for the purpose of centrifuging off solid components of the fluid, centrifuged in chambers from which, upon stopping the rotor, the fluid runs off due to gravity in canals leading centripetally obliquely downwardly. This device requires a considerable amount of space and, if one would think of using it for the control of the fluid flow, it involves the risk that a part of the fluid flows further in an uncontrollable manner through the relatively large canals.
Another problem of the known centrifugal analyzers is mixing up the fluid. It is very important for the analysis that the reagent and sample are mixed up in a short time and as completely as possible before they pass into the measurement cuvette. In order to achieve this, a number of improvements to centrifugal analyzers have already been suggested, for example the use of variously shaped flow impedances which are intended to improve the mixing of the fluid flowing through them. Another known device for mixing sample and reagent in a centrifugal analyzer is described in U.S. Pat. No. 3,795,451. The rotor thereof has a sample chamber which is separated by a vertical wall from the radially outward measurement cuvette. The upper end of the separating wall is provided with a passage the size of a capillary. Radially inwardly from the sample chamber, there is a reagent chamber, the separating wall between these being inclined obliquely downwardly and having on its lower end a passage with the dimensions of a capillary. In operation, the reagent is forced at a low speed of rotation into the sample chamber, which simultaneously serves as a mixing chamber. After a predetermined time, the speed of rotation is increased, the reaction solution thereby being forced out of the sample chamber into the cuvette. With such a device, mixing up of reagent and sample in the sample chamber is possibly improved, but a simultaneous control of the course of the reaction in the above-discussed sense for achieving multiple treatment of the reaction solution is not achieved and is also not an object of the described device.